Continuing Education Activity
Trimethoprim/sulfamethoxazole, also known as co-trimoxazole and can be abbreviated in the following ways: SXT, TMP-SMX, TMP-SMZ, or TMP-Sulfa. It is an antimicrobial used to treat and prevent many bacterial infections. This drug is very cost affordable and used for many types of illnesses. The FDA-Approved indications include acute infective exacerbation of chronic bronchitis, otitis media in pediatrics only, travelers diarrhea for treatment and prophylaxis, urinary tract infections, shigellosis, pneumocystis jirovecii, pneumonia/pneumocystis carinii pneumonia (PJP/PCP) both prophylactic and treatment, and toxoplasmosis both prophylactic and treatment. There are also non-FDA-approved indications. This activity outlines the indications, mechanism of action, methods of administration, important adverse effects, contraindications, toxicity, and monitoring, of TMP-SMX, so providers can direct patient therapy where necessary for infections as part of the interprofessional team.
- Identify the antimicrobial mechanism of action of trimethoprim/sulfamethoxazole, focusing on each component individually as well as the synergism of the combination.
- Summarize the approved indications for initiating antimicrobial therapy with trimethoprim/sulfamethoxazole.
- Outline the contraindications and adverse events associated with trimethoprim/sulfamethoxazole.
- Explain interprofessional team strategies for improving care coordination and communication to properly use trimethoprim/sulfamethoxazole to improve patient outcomes in infectious disease.
Trimethoprim/sulfamethoxazole, also known as co-trimoxazole and can be abbreviated in the following ways: SXT, TMP-SMX, TMP-SMZ, or TMP-Sulfa. It is an antimicrobial used to treat and prevent many bacterial infections. In 1974, TMP/SMX healthcare professionals began prescribing the medication, and the drug is now on the list of the World Health Organization's (WHO) essential medicines. This drug is very cost affordable and used for many types of illnesses.
The FDA-Approved Indications
- Acute infective exacerbation of chronic bronchitis
- Otitis media in pediatrics only
- Travelers diarrhea for treatment and prophylaxis
- Urinary tract infections
- Pneumocystis jirovecii pneumonia/Pneumocystis carinii pneumonia (PJP/PCP) both prophylactic and treatment
- Toxoplasmosis both prophylactic and treatment
The Non-FDA Approved Indications
- Prophylaxis in HIV-infected individuals
- Acne vulgaris
- Pertussis (whooping cough)
- Staphylococcus aureus infections, including methicillin-resistant Staphylococcus aureus (MRSA)
- Whipple disease
- Community-acquired pneumonia
Mechanism of Action
Sulfamethoxazole is a sulfonamide (antimicrobial drug class) that works directly on the synthesis of folate inside microbial organisms, e.g., bacteria. Sulfamethoxazole achieves this directly as a competitor of p-aminobenzoic acid (PABA) during the synthesis of dihydrofolate via inhibition of the enzyme dihydropteroate synthase. Trimethoprim is a direct competitor of the enzyme dihydrofolate reductase, causing its inhibition, which halts the production of tetrahydrofolate to its active form of folate. Tetrahydrofolate is a necessary component for the synthesis of purines required for DNA and protein production. When used alone, these drugs only act in a bacteriostatic manner. However, when used in the combination of sulfamethoxazole-trimethoprim, they block two steps in the bacterial biosynthesis of essential nucleic acids and proteins, thus can be bactericidal e.g., urine.
Sulfamethoxazole/trimethoprim may be administered orally without regard to meals. However, it is best to take it with at least 8 ounces of water. It also has an intravenous formulation. The choice of oral or intravenously varies both on the type of infection/or type of prophylactic use. It should not be administered intramuscularly. Patients with impaired renal function must have calculated dosing regimens based on renal function, as listed below. Administration of the two drugs is in a 1 to 5 ratio (trimethoprim:sulfamethoxazole) as a tablet formulation; this is so when they enter the body, their concentration throughout the blood/tissues is 1 to 20, which is the peak synergistic desired effect ratio of the two drugs in combination.
Oral dosage in adults and children weighing 40 kg (88 pounds) or more should have a single tablet of 800 mg of sulfamethoxazole and 160 mg of trimethoprim every 12 hours for 10 to 14 days. Children 2 months and older must have a weight-adjusted dosage.
Treatment of Pneumocystis jirovecii Pneumonia/Pneumocystis carinii Pneumonia
Adults/children, 2 months of age and older: The dose is also weight adjusted. Usually 75 to 100 mg per kilogram of body weight of sulfamethoxazole and 15 to 20 mg per kilogram body of body weight of trimethoprim each day for 14 to 21 days.
Prevention of Pneumocystis jirovecii pneumonia/ pneumocystis carinii pneumonia
In adults, 800 mg of sulfamethoxazole and 160 mg of trimethoprim is given once a day. In children, 2 months of age and older, dosages are determined by body size.
In adults, 800 mg of sulfamethoxazole and 160 mg of trimethoprim every 12 hours for 5 days. For children, 2 months and older use and dosage vary.
For acute exacerbations due to strains of Streptococcus pneumoniae or Haemophilus influenzae, one tablet of 800 mg of sulfamethoxazole and 160 mg of trimethoprim every 12 hours for 10 to 14 days.
Enteritis caused by Shigella flexneri and Shigella sonnei: 1 tablet 800 mg of sulfamethoxazole and 160 mg of trimethoprim every 12 hours for 5 days.
Urinary Tract Infections
One tablet 800 mg of sulfamethoxazole and 160 mg of trimethoprim every 12 hours for 14 days
One tablet 800 mg of sulfamethoxazole and 160 mg of trimethoprim every 12 hours for 14 days or 2 to 3 months if a chronic infection
Acne Vulgaris (Non-FDA Approved)
One tablet 800 mg of sulfamethoxazole and 160 mg of trimethoprim every 12 hours for 18 days
Community-Acquired Pneumonia (Non-FDA Approved)
One tablet 800 mg of sulfamethoxazole and 160 mg of trimethoprim every 12 hours for 10 to 14 days
Renal impairment guidelines are as follows:
- CrCl greater than 30 mL per minute no dose change
- CrCl 15 to 30 mL per minute decrease dose by 50%
- CrCl less than 15 do no use
Use is not recommended in children younger than 2 months of age.
The primary adverse effects of trimethoprim/sulfamethoxazole include rash, photosensitivity, as well as folate deficiency. A list of side effects are as follows:
- Loss of appetite
- Painful or swollen tongue
A patient with an unknown sulfa allergy then treated with trimethoprim/sulfamethoxazole may experience anaphylaxis or less serious yet severe symptoms such as hives, itchy eyes, swelling of the mouth and/or throat, and abdominal cramping.
- Known hypersensitivity to either drug or a past sulfa allergy
- Liver parenchymal damage, jaundice, and hepatic failure
- Hematological disorders
- Renal insufficiency
- Neonate less than 6 weeks of age
Trimethoprim/sulfamethoxazole is an American pregnancy category D medication. Use during early pregnancy has been related to congenital malformations and maternal folic acid deficiency; this may cause neural tube defects (spina bifida), urinary tract defects, oral clefts, and clubbed feet. Use during late pregnancy has been related to preterm labor. The drug also gets excreted in breast milk, and patients that are breastfeeding should not use trimethoprim/sulfamethoxazole during this time.
Administration of trimethoprim/sulfamethoxazole should not occur concomitantly with any of the following:
- ACE inhibitors: Risk of hyperkalemia
- Prilocaine: Risk of methemoglobinemia
- Antiarrhythmics: Risk of QTc prolongation
- Dapsone: Increases plasma levels of both drugs
- Methenamine: Risk of crystalluria
- Rifampin: Risk of reducing trimethoprim plasma concentrations
- Phenytoin: Increase in the half-life of phenytoin
- Antifolates: Risk of megaloblastic anemia
- Lamivudine, zalcitabine, and zidovudine
- Procainamide and/or amantadine
- Digoxin: Increase in digoxin levels
- Diuretics: Risk of thrombocytopenia
- Ciclosporin: Risk of kidney function decline
- Spironolactone: Risk of hyperkalemia
When initiating therapy with trimethoprim/sulfamethoxazole, some patients may require a baseline blood urea nitrogen and serum creatinine ratio, frequent complete blood counts (CBC), and electrolyte measurements if renal impairment is known or if taking a drug that has interactions with potassium.
Overdosing on trimethoprim/sulfamethoxazole is possible, and potential signs of toxicity include:
- Mental depression
- Loss of appetite
- Bone marrow depression
If there is suspicion of a patient having trimethoprim/sulfamethazine toxicity, a treatment plan includes the administration of activated charcoal (if ingested), gastric lavage, and supportive intravenous (IV) and oral fluids. More severe measures of treatment may consist of hemodialysis and alkalize the patient's urine.
Enhancing Healthcare Team Outcomes
Prescribing clinicians, including nurse practitioners, primary care providers, and internists who prescribe trimethoprim/sulfamethoxazole (TMP-SMX), should be familiar with ints indications and adverse effects. Also, when a patient receives a prescription of trimethoprim/sulfamethoxazole, some patients may need a baseline blood urea nitrogen and serum creatinine ratio, frequent complete blood counts (CBC), and electrolyte measurements if renal impairment is known or if taking a drug that has interactions with potassium.
Pharmacists should be consulted to verify coverage in conjunction with an infectious disease specialist, verify dosing, and perform medication reconciliation, and report any concerns to the rest of the healthcare team. Nurses will administer the drug inpatient and can also verify that there are no adverse events as a result of therapy with TMP-SMX, reporting any concerns immediately to the prescriber. In cases of pediatric use or renal impairment, the pharmacist, nurse, and prescriber should coordinate to ensure proper dosing. As with any medication therapy, antimicrobial treatment with TMP-SMX requires an interprofessional team approach, including physicians, specialists, specialty-trained nurses, and pharmacists, all collaborating across disciplines to achieve optimal patient outcomes. [Level V]